If you're talking about how it works in regards to the AMCAS April 30th deadline you just select "plan to enroll" rather than "commit to enroll". According to AMCAS this "plan to enroll" means that students can "...continue to interview, hold my current acceptance offers and receive additional acceptance offers, and remain on any waitlist at any other medical schools to which I applied". Whereas "commit to enroll" indicates that "...I have made my final selection and withdrawn all other applications, including waitlist positions".